Harvard Psychological Studies, Volume 1 eBook

The nature of the test in the experiments now to be
recorded is the same as the preceding, but a new box
was used. Fig. 2 is the floor plan and side view
of this apparatus. It was 44.5 cm. long, 23.5
cm. wide and 20 cm. deep. The partition at the
exit was 8.5 cm. in length. Instead of placing
this apparatus in the aquarium, as was done in the
previous experiments, a tray containing sand and water
was used to receive the animals as they escaped from
the box. The angle of inclination was also changed
to 7 deg.. For the triangular space in which
the animals were started in the preceding tests a rectangular
box was substituted, and from this an opening 8 cm.
wide by 5 cm. deep gave access to the main compartment
of the box.

A large healthy crawfish was selected and subjected
to tests in this apparatus in series of ten experiments
given in quick succession. One series a day was
given. After each test the floor was washed; as
a result the experiments were separated from one another
by a three-minute interval, and each series occupied
from thirty minutes to an hour. Table II. gives
in groups of five these series of ten observations
each. The groups, indicated by Roman numerals,
run from I. to IX., there being, therefore, 450 experiments
in all. Groups I. and II., or the first 100 experiments,
were made without having either of the exit passages
closed, in order to see whether the animal would develop
a habit of going out by one side or the other.
It did very quickly, as a matter of fact, get into
the habit of using the left passage (L.). The
last sixty experiments (Groups I. and II.) show not
a single case of escape by the right passage.
The left passage was now closed. Group III. gives
the result. The time column (i.e., the
third column of the table) gives for each series of
observations the average time in seconds occupied
by the animal in escaping from the box. It is
to be noted that the closing of the Left passage caused
an increase in the time from 30.9 seconds for the
last series of the second group to 90 seconds for
the first series of the third group. In this
there is unmistakable evidence of the influence of
the change in conditions. The animal after a
very few experiences under the new conditions began
going to the Right in most cases; and after 250 experiences
it had ceased to make mistakes. Group VII. indicates
only one mistake in fifty choices.